1. Field of the Invention
The invention relates to an asynchronous transfer mode (ATM) exchange and a method of operating the same.
2. Description of the Related Art
An asynchronous transfer mode (ATM) exchange is generally designed to include a server card and an Ethernet line card.
FIG. 1 is a block diagram of a server card 630 in a conventional ATM exchange, and FIG. 2 is a block diagram of an Ethernet line card 640 in a conventional ATM exchange. FIG. 3 illustrates a frame format used in communication between the server card 630 and the Ethernet line card 640.
As illustrated in FIG. 1, the server card 630 is comprised of a first reassembly unit 601, a second unit 602 for retrieving a routing table, a third unit 603 for producing connection data, a fourth unit 604 for producing a MAC address, and a fifth unit 605 for carrying out segmentation.
The first reassembly unit 601 receives an ATM cell 11, converts the thus received ATM cell 11 into an IP packet 32, and transmits the thus converted IP packet 32 to the second unit 602. The second unit 602 receives the IP packet 32 from the first unit 601, and extracts an IP next hop 41 out of the IP packet 32. The thus extracted IP packet 32 is transmitted to both the third unit 603 and the fourth unit 604, and the IP packet 32 received by the second unit 602 is transmitted to the fifth unit 605.
The third unit 603 converts the thus received IP next hop 41 into connection data 42, and the fourth unit 604 converts the thus received IP next hop 41 into a MAC (Media Access Control) address 43. The thus produced connection data 42 and MAC address 43 are transmitted to the fifth unit 605. The fifth unit 605 converts the IP packet 32 into an output ATM cell 11a, based on the connection data 42 and the MAC address 43.
As illustrated in FIG. 2, the Ethernet line card 640 is comprised of a second reassembly unit 606 and a sixth unit 607 for producing an Ethernet frame.
The second reassembly unit 606 receives an ATM cell 11, and converts the ATM cell into an IP packet 32. The sixth unit 607 receives the IP packet 32 from the second reassembly unit 606, and converts the IP packet 32 into an Ethernet frame 34.
The server card 630 and the Ethernet line card 640 make communication with each other through a frame format illustrated in FIG. 3, for instance.
However, the above-mentioned conventional ATM exchange is accompanied with a problem that an extremely high load is exerted on the server card 630, because the server card 630 has to convert the IP next hop 41 into both the connection data 42 and the MAC address 43.
In addition, since the frame format illustrated in FIG. 3, used for making communication between the server card 630 and the Ethernet line card 640 has a different structure from a structure of a frame format used for transmitting an IP packet on ATM, the server card 630 has to operate in different ways in dependence on whether an output therefrom is to be transmitted through ATM or through Ethernet.
Japanese Unexamined Patent Publication No. 11-215156 has suggested a connector for connecting communication networks to each other among ATM and non-ATM networks. The connector includes a first network connector for connecting a first non-ATM network to an ATM network, and a second network connector for connecting the ATM network to a second non-ATM network. When data is to be transmitted from a first terminal connected to the first non-ATM network to a second terminal connected to the second non-ATM network through the ATM network, data is transmitted based on MAC (Media Access Control) address of the second terminal, after communication link has been established between the first and second network connectors.
Japanese Unexamined Patent Publication No. 11-289345 has suggested a router for determining a route through which data is transmitted when networks are connected to each other. The router is comprised of a routing table, a cache table, and a cache management table. The routing table stores a network address as an IP address indicative of an address of a network to which data is to be transmitted, a next hop address as an IP address of a router to which data is to be transmitted, and a transmission interface number. The cache table stores data about a link layer (MAC header) as an IP address of an address of a host, and a transmission interface number. A routing entry number is assigned to each entry in the routing table, and a cache entry number is assigned to each entry in the cache table. The cache management table stores data indicative of a relation between the routing entry number and the cache entry number.
Japanese Patent No. 2891146 (Japanese Unexamined Patent Publication No. 9-116560) has suggested a network server which accomplishes virtual LAN including existing LAN terminals on ATM network regardless of locations of the LAN terminals. The network server includes a LAN terminator which terminates a protocol of a MAC sub-layer in an existing LAN, an ATM terminator which terminates protocols of AAL and ATM, and a data transmitter which transmits data to a terminator associated with a MAC address identified based on data received in any one of the terminators, an identifier checker which identifies an Ether type of data received in any one of the terminators, and means for, when the data is transmitted to an ATM terminator, determining ATM connection through which data is to be transmitted, based on a MAC address, an IP sub-net address, and the Ether type, and notifying the ATM connection to the ATM terminator.
Japanese Unexamined Patent Publication No. 10-303965 has suggested a router including RFC 1577 “Classical IP and ARP over ATM”, having a virtual interface, and operating in ATM-LAN atmosphere. The router includes an address table. An entry comprised of an address in a network layer, an address of a next hop on a patch through which a packet is transmitted, and data about packet transmission can be registered into the address table, retrieved in the address table, or deleted from the address table. The address in a network layer and the address of a next hop are registered as data about packet transmission when a packet is to be transmitted. A header in a data link layer and an interface to which data is to be transmitted are registered as data about packet transmission when data is to be transmitted to a LAN interface. Data about calls in ATM is registered as data about packet transmission when data is to be transmitted to an ATM interface. Data is transmitted directly to a physical interface without carrying out a routing step, by using the address table in which packets having been received from the interfaces are registered.
Japanese Unexamined Patent Publication No. 8-79294 has suggested a an apparatus of connecting LAN terminals to each other or connecting a LAN terminal to an ATM terminal through an ATM network. The apparatus includes a protocol converter between an ATM network and each of LANs.
Japanese Unexamined Patent Publication No. 7-264207 has suggested a method of connecting a terminal to an ATM network. In the method, an ATM adapter, which interactively converts a data field and an address field in a packet transmitted between terminals in non-ATM LAN to a data field and a header in an ATM cell transmitted in an ATM network having at least one an ATM exchange, is arranged either in the data terminals or between the data terminal and the ATM exchange. The data terminal in a non-ATM LAN is connected to the ATM network through the ATM adapter.
Japanese Unexamined Patent Publication No. 7-74782, which is based on the U.S. application Ser. No. 058157 filed by Ken Marshal on May 5, 1993, has suggested an apparatus for transmitting data from non-ATM terminal to an ATM terminal. The apparatus is comprised of a non-ATM communication interface which is connected to the non-ATM terminal and which receives non-ATM communication data packet from the non-ATM terminal, segmentation means connected to the non-ATM communication interface for dividing the non-ATM communication data packet into ATM cells after the non-ATM communication interface has received the non-ATM communication data packet, and an ATM interface connected to both the ATM terminal and the segmentation means for transmitting the ATM cell through the ATM terminal in response to the segmentation means.
However, the above-mentioned problems remain unsolved even in the above-mentioned Publications.